共查询到20条相似文献,搜索用时 521 毫秒
1.
Sebastian Geiger Thomas Driesner Christoph A. Heinrich Stephan K. Matthäi 《Transport in Porous Media》2006,63(3):435-461
We present the benchmarking of a new finite element – finite volume (FEFV) solution technique capable of modeling transient
multiphase thermohaline convection for geological realistic p-T-X conditions. The algorithm embeds a new and accurate equation of state for the NaCl–H2O system. Benchmarks are carried out to compare the numerical results for the various component-processes of multiphase thermohaline
convection. They include simulations of (i) convection driven by temperature and/or concentration gradients in a single-phase
fluid (i.e., the Elder problem, thermal convection at different Rayleigh numbers, and a free thermohaline convection example),
(ii) multiphase flow (i.e., the Buckley–Leverett problem), and (iii) energy transport in a pure H2O fluid at liquid, vapor, supercritical, and two-phase conditions (i.e., comparison to the U.S. Geological Survey Code HYDROTHERM).
The results produced with the new FEFV technique are in good agreement with the reference solutions. We further present the
application of the FEFV technique to the simulation of thermohaline convection of a 400°C hot and 10 wt.% saline fluid rising
from 4 km depth. During the buoyant rise, the fluid boils and separates into a high-density, high-salinity liquid phase and
a low-density, low-salinity vapor phase. 相似文献
2.
A. F. Glukhov V. A. Demin G. F. Putin 《Journal of Applied Mechanics and Technical Physics》2009,50(1):58-65
The stationary modes of thermal convection of a binary mixture in connected channels of finite height were studied experimentally
and theoretically. The effects of positive and negative thermal diffusion on the convection were examined. The ranges of parameters
corresponding to the modes of soft and rigid initiation of convection were determined. Vertical distributions of the temperature
and concentration fields were found for various values of the thermal diffusion parameter.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 1, pp. 68–77, January–February, 2009. 相似文献
3.
The mixed convection in a vertical plane-parallel channel with two heat sources of finite dimensions located at the wall is
analyzed on the basis of a two-dimensional numerical simulation. The effect of the distance between the heat sources on the
flow pattern and the temperature field is studied. Calculations are performed on the Grashof and Reynolds number ranges from
0–105 and 0–10, respectively, at a Prandtl number of 0.7. The mathematical model is based on the time-dependent Navier-Stokes equations
in the Boussinesq approximation. The problem is solved by the finite element method. 相似文献
4.
In this study, a numerical methodology for the solution of conjugate heat and mass transfer problem is presented. Fluid flow,
heat and mass transfer over a rectangular brick due to transient laminar mixed convection has been numerically simulated.
The coupled non-linear partial differential equations, for both gas phase and solid are solved using finite element procedure.
Flow is assumed to be incompressible, two-dimensional, laminar. Analysis has been carried out at a Reynolds number of 200
with Pr = 0.71. The effect of buoyancy on the brick drying has been investigated. Velocity vectors, streamlines in the flow
field and temperature and moisture contours and temperature distribution along the solid surface are presented. It is observed
that there is considerable effect of buoyancy during drying. The results indicate a non-uniform drying of the brick with the
leading edge drying faster than the rest of the brick.
Received on 9 December 1998 相似文献
5.
Björn Johannesson 《Transport in Porous Media》2010,85(2):565-592
A numerical scheme for the transient solution of a generalized version of the Poisson–Nernst–Planck (PNP) equations is presented.
The finite element method is used to establish the coupled non-linear matrix system of equations capable of solving the present
problem iteratively. The PNP equations represent a set of diffusion equations for charged species, i.e. dissolved ions, present
in the pore solution of a rigid porous material in which the surface charge can be assumed neglectable. These equations are
coupled to the ‘internally’ induced electrical field and to the velocity field of the fluid. The Nernst–Planck equations describing
the diffusion of the ionic species and Gauss’ law in use are, however, coupled in both directions. The governing set of equations
is derived from a simplified version of the so-called hybrid mixture theory (HMT). The simplifications used here mainly concerns
ignoring the deformation and stresses in the porous material in which the ionic diffusion occurs. The HMT is a special version
of the more ‘classical’ continuum mixture theories in the sense that it works with averaged equations at macroscale and that
it includes the volume fractions of phases in its structure. The background to the PNP equations can by the HMT approach be
described by using the postulates of mass conservation of constituents together with Gauss’ law used together with consistent
constitutive laws. The HMT theory includes the constituent forms of the quasistatic version of Maxwell’s equations making
it suitable for analyses of the kind addressed in this work. Within the framework of HTM, constitutive equations have been
derived using the postulate of entropy inequality together with the technique of identifying properties by Lagrange multipliers.
These results will be used in obtaining a closed set of equations for the present problem. 相似文献
6.
A finite volume element method is developed for analyzing unsteady scalar reaction-diffusion problems in two dimensions. The method combines the concepts that are employed in the finite volume and the finite element method together. The finite volume method is used to discretize the unsteady reaction-diffusion equation, while the finite element method is applied to estimate the gradient quantities at cell faces. Robustness and efficiency of the combined method have been evaluated on uniform rectangular grids by using available numerical solutions of the two-dimensional reaction-diffusion problems. The numerical solutions demonstrate that the combined method is stable and can provide accurate solution without spurious oscillation along the high-gradient boundary layers. 相似文献
7.
In this study, we carried out a numerical simulation of transient heat transfer in a composite passive system consisting of
air–phase change material–air, arranged as a rectangular enclosure. The vertical boundaries of the enclosure are isothermal
and the horizontal ones adiabatic. The enthalpy formulation with a fixed grid is used to study the process of phase change
with liquid–solid interface zone controlled by natural convection. The flow in this zone is simulated by a model based on
the Darcy porous medium. The numerical solution of the mathematical model is done using finite difference–control volume algorithm.
The influence of the geometrical and thermal parameters is studied. It is found that subcooling coefficient is the most important
parameter influencing heat transfer, and for a given subcooling, there is an optimum phase change partition thickness. 相似文献
8.
M. NEJAD M. Z. SAGHIR M. R. ISLAM 《International Journal of Computational Fluid Dynamics》2013,27(2):157-168
In this paper, thermal diffusion phenomena in a porous cavity are investigated. The Brinkman model, coupled with the energy and the mass balance equations was solved numerically using a finite element techniques. A two-component system was included in the model. Different models were investigated to demonstrate the importance of the Soret effect with the presence of gravity vector. We do not take into consideration the pressure effect in the thermal diffusion. Even with such simplification to the problem, results reveal that the thermal diffusion is important and drives a strong convection. A series of convection cells are observed and steady-state solutions are obtained. Asymmetric solutions are obtained for various cases of dual-porosity porous media. Variations in the gravity vector indicated that the convection patterns, as well as the role of Soret coefficient, are profoundly impacted. Finally, the importance of including thermal diffusion in petroleum reservoir simulation is discussed. 相似文献
9.
The present paper deals with the determination of permeability in partially saturated conditions for weakly permeable porous
rocks such as argillites or deep clayey formations. The level of permeability can be obtained via the measurements of transient
weight loss of a sample submitted to a decrease in relative humidity imposed by saline solution in a hermetic chamber. An
identification method based on simplified uncoupled 1D-linear and 1D-non-linear modelling was presented in a previous paper
(Giraud et al. Trans Porous Media 69(2):259–280, 2006). The present paper takes into account generalized mass transfer phenomena
such as Darcean advective transport of liquid and gas mixtures and Fickean diffusive transport of the vapour specie inside
a gas mixture. Poromechanical coupling as well as 3D effects due to the geometry and finite dimensions of the tested samples
are also covered by this approach. The coupled THM finite element computer code Code_Aster is then used to model the forward problem. The parameter identification procedure is based upon the solution of an inverse
problem. The Levenberg–Marquardt algorithm was used for the problem of minimization. Comparisons between previous simplified
1D modelling and 2D-axisymmetrical coupled modelling show that the former method efficiently provides the correct order of
magnitude of the level of permeability or the equivalent storage coefficients. Due to the boundary condition, the real 2D-axisymmetrical
geometry of the sample must not be neglected if we are to obtain accurate results. 相似文献
10.
In this paper a thick hollow cylinder with finite length made of two dimensional functionally graded material (2D-FGM) subjected
to transient thermal boundary conditions is considered. The volume fraction distribution of materials, geometry and thermal
boundary conditions are assumed to be axisymmetric but not uniform along the axial direction. The finite element method with
graded material properties within each element is used to model the structure and the Crank–Nicolson finite difference method
is implemented to solve time dependent equations of the heat transfer problem. Two-dimensional heat conduction in the cylinder
is considered and variation of temperature with time as well as temperature distribution through the cylinder are investigated.
Effects of variation of material distribution in two radial and axial directions on the temperature distribution and time
response are studied. The achieved results show that using two-dimensional FGM leads to a more flexible design so that transient
temperature, maximum amplitude and uniformity of temperature distributions can be modified to achieve required specifications
by selecting a suitable material distribution profile in two directions. 相似文献
11.
We investigate the effectiveness of the partition‐of‐unity method (PUM) for convection–diffusion problems. We show that for the linear diffusion equation, an exponential enrichment function based on an approximation of the analytic solution leads to improved accuracy compared to the standard finite‐element method. It is illustrated that this approach can be more efficient than using polynomial enrichment to increase the order of the scheme. We argue that the PUM enrichment, can be interpreted as a subgrid‐scale model in a multiscale framework, and that the choice of enrichment function has consequences for the stabilization properties of the method. The exponential enrichment is shown to function as a near optimal subgrid‐scale model for linear convection. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
12.
A. Pantokratoras 《Heat and Mass Transfer》2000,36(4):351-360
In most studies concerning laminar natural convection along a vertical isothermal cylinder a linear relationship between
fluid density and temperature has been used and kinematic viscosity and thermal diffusivity have been considered constant
calculated at ambient temperature. However, it is known that the density–temperature relationship for water is non-linear
at low temperatures and kinematic viscosity and thermal diffusivity are functions of temperature. In this study the problem
of laminar natural convection of pure and saline water along a vertical isothermal cylinder has been investigated in the temperature
range between 20 and 0 ∘C taking into account the temperature dependence of ν, α and ρ. The results are obtained with the numerical solution of the
boundary layer equations. The variation of ν, α and ρ with temperature has a strong influence on free convection characteristics.
Received on 17 May 1999 相似文献
13.
J. Szimmat 《Heat and Mass Transfer》2002,38(4-5):279-293
The present work deals with the development and application of numerical models for the simulation of solidification problems liquid/solid taking diffusion and convection into account. For the calculation of the thermal coupled flow process the finite element method is applied. In order to improve the numerical stability of the free convection problems, the streamline-upwind/Petrov–Galerkin method is used. Solidification processes are moving boundary problems. Three different models are set up which consider latent heat at the solidification front respectively in the mixed zone during the phase transition. Moreover, numerical methods are investigated in order to describe the behaviour of the flow at the boundary of the moving phase. Three examples serve illustrations; the technical example – casting of a transport and storage container – was provided by the company Siempelkamp Gießerei GmbH. 相似文献
14.
Sebastian Geiger Thomas Driesner Christoph A. Heinrich Stephan K. Matthäi 《Transport in Porous Media》2006,63(3):399-434
We present a new finite element – finite volume (FEFV) method combined with a realistic equation of state for NaCl–H2O to model fluid convection driven by temperature and salinity gradients. This method can deal with the nonlinear variations
in fluid properties, separation of a saline fluid into a high-density, high-salinity brine phase and low-density, low-salinity
vapor phase well above the critical point of pure H2O, and geometrically complex geological structures. Similar to the well-known implicit pressure explicit saturation formulation,
this approach decouples the governing equations. We formulate a fluid pressure equation that is solved using an implicit finite
element method. We derive the fluid velocities from the updated pressure field and employ them in a higher-order, mass conserving
finite volume formulation to solve hyperbolic parts of the conservation laws. The parabolic parts are solved by finite element
methods. This FEFV method provides for geometric flexibility and numerical efficiency. The equation of state for NaCl–H2O is valid from 0 to 750°C, 0 to 4000 bar, and 0–100 wt.% NaCl. This allows the simulation of thermohaline convection in high-temperature
and high-pressure environments, such as continental or oceanic hydrothermal systems where phase separation is common. 相似文献
15.
Analysis of Pore Pressure Distribution in Shale Formations under Hydraulic,Chemical, Thermal and Electrical Interactions 总被引:1,自引:0,他引:1
Change in pore pressure in chemically active rocks such as shale is caused by several mechanisms and numerous studies have
been carried out to investigate these mechanisms. However, some important coupling terms or driving forces have been neglected
in these studies due to simplifying assumptions. In this study, a hydro-chemo-thermo-electrical model based on finite element
method is presented to investigate the change in pore pressure in shale formations resulted from thermal, hydraulic, chemical
and electric potential gradients. The change in pore pressure is induced by hydraulic conduction, chemical, electrical and
thermal osmotic flow. In order to solve the problem of ion transfer under the influence of an electrical field, the Nernst–Planck
equation is used. In addition, ion advection is considered to investigate its possible effect on ion transfer for the range
of shale permeability. All equations are derived based on the thermodynamics of irreversible processes in a discontinuous
system. The numerical results are compared against existing and derived uncoupled analytical solutions and good agreement
is observed. The numerical results showed that the ion transfer and pore pressure are considerably affected by the electric
field in the vicinity of the wellbore. It was also found that advection can play a remarkable role in ion transfer in shale
formations. It was further shown that the change in pore pressure in shale formation is characterized by the combined effect
of hydraulic, chemical, thermal and electro osmotic flow. 相似文献
16.
ntroductionLetΩ R2 beaboundeddomain .Weconsiderthefollowingnon_stationarynaturalconvectionproblem :Problem (Ⅰ ) Findu =(u1,u2 ) ,p ,andTsuchthat,foranyt1>0 ,ut- μΔu +(u· )u + p=λjT ((x ,y ,t) ∈Ω× (0 ,t1) ) ,divu =0 ((x ,y,t) ∈Ω× (0 ,t1) ) ,Tt-ΔT +λu· T =0 ((x,y,t) ∈Ω× (0 ,t1) ) ,u =0 ,T =0 ((x,y,t)∈ Ω× (0 ,t1) ) ,u(x ,y ,0 ) =0 , T(x,y,0 ) =f(x,y) ((x,y) ∈Ω) ,whereuisthefluidvelocityvectorfield ,pthepressurefield ,Tthet… 相似文献
17.
Asterios Pantokratoras 《Meccanica》2017,52(6):1491-1492
A numerical investigation of transient magnetohydrodynamic free convection flow past an infinite vertical plate embedded in a porous medium with viscous dissipation is presented in the above paper. The governing differential equations are transformed into a set of non-linear coupled partial differential equations and are solved numerically using the finite element method. Numerical results for the velocity, temperature and concentration profiles within the boundary layer are presented and discussed. 相似文献
18.
The aim of the work is to present a detailed numerical study of the transient forced laminar convection flow over a flat
plate, when thermal conditions are due to arbitrary wall heat flux variations in space. The energy governing equation is modelled
using the Karman–Pohlhausen integral approach in the wide range of Prandtl numbers. The influence of both the thermal problem
nature (transient heating and/or cooling processes) and the wall flux function on the resulting mathematical expressions is
evidenced and the thermal boundary layer thickness behaviour is discussed. In addition, a particular attention has been focused
on both the change in sign of the flux and the duration of the transient heating and cooling. Detailed thermal responses and
convective heat coefficient evolutions due to the change of wall conditions are presented.
Received on 14 April 2000 / Published online: 29 November 2001 相似文献
19.
A nodeless variable element method with the fluxbased formulation is developed to analyze two-dimensional thermal-structural problems. The nodeless variable formula- tion provides accurate temperature distributions to yield more accurate thermal stress solutions. The flux-based formulation is used to reduce the complexity in deriving the finite element equations as compared to the conventional finite element method. The solution accuracy is further improved by implementing an adaptive meshing technique to generate finite element meshes that can adapt and move along with the transient solution behavior. A version of a nearly optimal element size determination is proposed to provide high convergence rate of the predicted solutions. The combined procedure is evaluated by solving several thermal, structural, and thermal stress problems. 相似文献
20.
浮区法因具有无坩埚接触污染的生长优点而成为生长高完整性和高均匀性单晶材料的重要技术.但熔体中存在的毛细对流会给浮区法晶体生长带来极大挑战,这是由于对流的不稳定会导致晶体微观瑕疵的产生和宏观条纹等缺陷的形成.为了提高浮区法生长单晶材料的品质,研究浮区法晶体生长中毛细对流特性及如何控制其不稳定性显得尤为重要.本文采用数值模拟的方法对半浮区液桥内SixGe1-x体系中存在的热质毛细对流展开研究并施加旋转磁场对其进行控制.结果表明:纯溶质毛细对流表现为二维轴对称模式,温度场主要由热扩散作用决定,而浓度场则由对流和溶质扩散共同支配;纯热毛细对流呈现三维稳态非轴对称流动,浓度分布与熔体内热毛细对流的流向密切相关,等温线在对流较大的区域发生弯曲;耦合溶质与热毛细对流则为三维周期性旋转振荡流.施加旋转磁场后,熔体周向速度沿径向向外增大,熔体内浓度场和流场均呈现二维轴对称分布. 相似文献